A particular problem of water pumping in remote areas is the provision of power to the pump. The provision of mains electricity is often expensive and only economic if only a short extension of the power lines is required or for particularly large installations. Diesel generators provide a predictable output but require regular maintenance and refuelling. Windmills generally provide good service in suitable locations but their output is affected by wind droughts and they require regular maintenance. Solar-powered pumps are therefore advantageous and are particularly cost-effective when there is a lower power requirement, the site is remote and has no reliable electricity supply.
An important factor in maximising the efficiency of a solar-powered pumping array is to maximise the conversion of sunlight to electricity. Motors with an efficiency of 90% or more and pumps with an efficiency of 70% or more are available but solar cell arrays often have an efficiency of less than 15%. The efficiency of a solar cell array can be maximised by accurately pointing the array at the sun. Known electronic tracking systems utilise light sensitive sensors that measure incoming solar radiation or light. Two opposing sensors ate placed on the solar array at opposing angles to the array's perpendicular. The array frame is then driven via a motor to balance the signal between the two sensors. This system does not have a great reliability record as the sensors must be mounted in direct sunlight, which can lead to degradation over time. The sensors must be connected to an electronic controller via an electrical wiring loom, which is routed around the array frame. External sensors have a history of being broken off accidentally, either in transport or in day to day use. These systems can also incorporate electrical stops and sensors to detect motor positions and end stops, which also have long term reliability problems as they are continuously exposed to the weather.
Another type of system utilises gas-filled tanks or a gas-filled frame as a method of positioning the solar array. As the solar radiation heats up the array, the gas transfers from one side of the array to the other, moving the array frame until the system is in a balanced state directed towards the sun. Such gas trackers have been found to have reliability issues with gas leaks and system imbalances causing erratic operation. This system is also very difficult to manufacture and transport as the system is very bulky and heavy.
Both of the above-described systems do not perform adequately in cloudy or low light conditions, as the amount of solar radiation is limited on these occasions.
To counteract low light problems, electronic solar trackers can use a time clock to keep track of the sun position but then an accurate time base is required, otherwise a cumulative time error can produce a large error over years of operation. It is also necessary to initially set the time and adjust the system for the location of the device, which can introduce errors.